1. Field of the Invention
The present invention generally relates to a electrophotographic color image forming apparatus such as a color photocopier or a color printer, having a plurality of electrophotographic developing devices, and more particularly, to a voltage supply apparatus of the developing device to supply high voltage to the plurality of developing devices for color printing or color photocopying.
2. Description of the Related Art
FIG. 1 shows a general conventional electrophotographic color image forming apparatus 10 such as a color photocopier or a color printer, having a photoreceptor body 11 formed in a drum shape which is continuously revolved in a predetermined direction by a driving source (not shown).
Formed in a proximity of an outer circumference of the photoreceptor body 11 are: a charging unit 12, a laser scanning unit (LSU) 20, four slidable developer units 31, 32, 33 and 34 as yellow, magenta, cyan and black slidable units, respectively, each containing developers representing yellow, magenta, cyan and black colors, respectively, a transfer transporting portion 60, an erasing lamp 87 and a cleaning discharging portion 80, all formed in a successive order of a rotational direction of the photosensitive body 11.
The charging unit 12 may be a scrotron, and may evenly charges the photoreceptor body 11. The LSU 20 exposes the photoreceptor body 11 to a light source such as a laser source axially in a linear fashion.
Each of the slidable developer units 31, 32, 33 and 34 includes a developer roller 13, a developer reservoir 16, a developer feeding roller 15 and a developer layer thickness regulating member, for example, a blade 51 that regulates a thickness of the developer attached onto the developer roller 13. The slidable developer units 31, 32, 33 and 34 are driven by a developer driving source (not shown), respectively. A developer is fed to the developer roller 13 through the developer feeding roller 15 of the developer reservoir 16 and a predetermined high voltage is applied. The thickness of the developer on the developer roller 13 is regulated to be thin by the developer layer thickness regulating member 51 that applies a predetermined voltage for an electric charge supply.
The respective slider developer units 31, 32, 33 and 34 are slidable, and are movably supported to reciprocate in a developer guiding member (not shown). The slidable developer units 31, 32, 33 and 34 are each moved toward the photoreceptor body 11 and against releasing springs 74 by first to fourth eccentric cams 35, 36, 37 and 38 which are fixed on rotary axes 56. A rotation of the rotary axes 56 is controlled by an electric clutch (not shown).
During a developing process, a developing bias voltage is applied to the developer roller 13. With a negative-positive reversal process, the developing bias voltage becomes identical to a charging polarity of the photoreceptor body 11.
The transfer transporting portion 60 electro magnetically transfers a color image on the photoreceptor body 11 onto a recording medium such as a paper P, and the cleaning discharging portion 80 removes remaining developer from the photoreceptor body 11.
An operation of the image forming apparatus 10 as above constructed is described in detail. With a reception of a printing command, the photoreceptor body 11 is continuously revolved by a photoreceptor driving source (not shown), during which a surface of the photoreceptor body 11 is evenly charged by the charging unit 12. When a charged region reaches a yellow image developing position (d) of the yellow developer unit 31 for a color image to first form, for example, a yellow image, the electric clutch of the yellow slidable developer unit 31 is turned on, and the yellow slidable developer unit 31 is moved toward the photoreceptor body 11 to be set in a developing state.
The surface of the photoreceptor body 11 is exposed to the LSU 20, thereby having a yellow electrostatic latent image formed thereon. In the yellow image developing position (d), the yellow image is continuously formed from a leading to a tail end of the color image by the yellow slidable developer unit 31.
With a completion of the yellow image and passing of the tail end of the yellow image through the yellow image developing position (d), the first eccentric cam 35 rotates thereby causing the yellow slidable developer unit 31 to separate apart from the photoreceptor body 11.
As the leading end of the yellow image reaches a magenta image developing position (e) of the magenta slidable developer unit 32, for a color image to secondly form, for example, a magenta image, the electric clutch of the magenta slidable developer unit 32 turns on. Accordingly, the magenta slidable developer unit 32 is set by the second eccentric cam 36 to a developing state.
The yellow image on the photoreceptor body 11 is passed through the transfer transporting portion 60, the erasing lamp 87 and the cleaning discharging portion 80 which are not in operation, and positioned below the charging unit 12. The transfer transporting portion 60 and the cleaning discharging portion 80 are formed so as not to contact with the photoreceptor body 11 to prevent a smearing of the image passing therebetween.
The photoreceptor body 11 having the yellow image formed thereon under the charging unit 12 is again uniformly charged by the charging unit 12, and the magenta image is overlapped on the yellow image by exposing the photoreceptor body 11 to light from the LSU 20, and developed in the magenta image developing position (e) by the magenta slidable developer unit 32. With a completion of forming of the magenta image, the tail end of the image passes through the magenta image developing position (e), and the second eccentric cam 36 rotates. As a result, the magenta developer unit 32 is separated apart from the photoreceptor body 11.
When the leading end of the image reaches a cyan image developing position (f) of the cyan slidable developer unit 33 for a color image to be thirdly formed, for example, a cyan image, an electric clutch of the cyan slidable developer unit 33 turns on so that the cyan slidable developer unit 33 is set at a developing state.
A composite image of the yellow and magenta images passes through the transfer transporting portion 60 and the erasing lamp 87 and is positioned below the charging unit 12. The photoreceptor body 11 is evenly (i.e., uniformly) charged by the charging unit 12. The composite image of the yellow and magenta images is overlapped with the cyan image by exposing the photoreceptor body 11 to light from the LSU 20, and developed in the cyan image developing position (f) by the cyan slidable developer unit 33. After a completion of the forming of cyan image, the tail end of the image is passed through the cyan image developing position (f), the third eccentric cam 37, rotates and the cyan slidable developer unit 33 is separated apart from the photoreceptor body 11.
A black image is overlapped and formed in a same way described above, thus forming of an entire image is complete. That is, when the leading end of the image reaches a black image developing position (g) of the black slidable developer unit 34 for a color image to be fourthly formed, for example, a black image, an electric clutch of the black slidable developer unit 34 turns on so that the black slidable developer unit 34 is set at a developing state. The color image on the photoreceptor body 11 is transferred by the transfer transporting portion 60 to a recording medium P, which is synchronously transported from a recording medium feeding portion.
After the image transfer, the photoreceptor body 11 is discharged by the erasing lamp 87, and as a remaining developer on the surface of the photoreceptor body 11 is removed by a rotary brush 81 of the cleaning discharging portion 80, the photoreceptor body 11 returns to an initial state. The recording medium P with the color image formed thereon is transported to the recording medium fusing portion (not shown), and after the colors are fixed on the recording medium P at the recording medium fusing portion, the recording medium P is discharged externally.
With the construction of the conventional photoelectrographic color image forming apparatus 10 as described above, since the four slidable developer units 31, 32, 33 and 34 are brought to contact with the photoreceptor body 11 under a predetermined pressure, or slid away from the photoreceptor body 11, the photoreceptor body 11 is in contact with the developer rollers 13 of the four slidable developer units 31, 32, 33 and 34 four times during one cycle of the photoreceptor body 11.
As shown in FIG. 2, power supply sliding contact-point terminals 13a, 15a and 51a connected to the developer rollers 13, the developer feeding rollers 15 and the developer layer thickness regulating members 51 of the four slidable developer units 31, 32, 33 and 34 are sequentially connected to, or disconnected from, stationary contact-point terminals 90a′, 90b′, 90c′, respectively, which are connected to corresponding voltage supplies of high voltage power supply (HVPS) 90, i.e., to a developer roller voltage unit 90a, a developer feeding roller voltage unit 90b and a developer layer thickness regulating blade voltage unit 90c through a complex wiring harness.
However, in the conventional electrophotographic color image forming apparatus 10 constructed as above, complicated structures of the first to fourth eccentric cams 35, 36, 37 and 38, cam driving motors (not shown) and the electric clutches are required for a sequential use of the four slidable developer units 31, 32, 33 and 34.
Further, a shock is generated from the contact of the photoreceptor body 11 with the developer rollers 13 of the four slidable developer units 31, 32, 33 and 34 at a time of changing from one slidable developer unit 31, 32, 33 or 34 to another slidable developer unit 31, 32, 33 or 34, and the shock is directly transmitted to the photoreceptor body 11 in a developing process. Thus, a lifespan of the photoreceptor body 11 is shortened, and the photoreceptor body 11 is subjected to speed changes, and jittering occurs deteriorating printing quality.
Further, a power supply apparatus supplying a high voltage to the slidable developer units 31, 32, 33 and 34 of the conventional electrophotographic color image forming apparatus 10 has a complicated construction in which the voltage units 90a, 90b and 90c of the HVPS 90 are connected with the stationary contact-point terminals 90a′, 90b′ and 90c′, respectively, through the complex wiring harness causing a complicated manufacture process. Further, a sliding contact of the sliding contact-point terminals 13a, 15a and 51a with the stationary contact-point terminals 90a′, 90b′ and 90c′ causes a degradation of a reliability in switching of high voltage contact-points.
To overcome the above-mentioned problems of the conventional electrophotographic color image forming apparatus 10 using the above sliding type developer units 31, 32, 33 and 34, is an image forming apparatus (not shown) having stationary developer units 31′, 32′, 33′ and 34′ secured in a spaced-apart relation with a photoreceptor body to have a predetermined gap, i.e., 0.2 mm (see FIGS. 3 and 4).
The image forming apparatus includes a HVPS 90′ having a developer roller voltage unit 90d, a developer feeding roller voltage unit 90e, and a developer layer thickness regulating member voltage unit 90f; stationary contact-point terminals 13a′, 15a′ and 51a′ of the stationary developer units 31′, 32′, 33′ and 34′ secured at the predetermined gap with respect to the photoreceptor body instead of either contacting or isolating the stationary developer units 31′, 32′, 33′ and 34′ with respect to the photoreceptor body 11; and a coupling printed circuit board (PCB) 95 that connects the voltage units 90d, 90e and 90f of the HVPS 90′ with the stationary contact-point terminals 13a′, 15a′ and 51a′ of the stationary developer units 31′, 32′, 33′ and 34′.
The coupling PCB 95 includes: first, second and third PCB input terminals 95d, 95e and 95f connected with the voltage units 90d, 90e and 90f of the HVPS 90′ through wiring harnesses; first, second and third PCB output terminals 95d′, 95e′ and 95f′ connected to corresponding stationary contact-point terminals 13a′, 15a′ and 51a′ of the respective stationary developer units 31′, 32′, 33′ and 34′ through first, second and third spring terminals 98d, 98e and 98f of the respective stationary developer units 31′, 32′ 33′ and 34′; and four solenoids 91 each having first, second and third solenoid input terminals 91d, 91e and 91f, which are connected to the first, second and third PCB input terminals 95d, 95e and 95f, respectively, through a connecting line patterned in the coupling PCB 95, and first, second and third output switching terminals 91d′, 91e′ and 91f′ connected to the first, second and third PCB output terminals 95d′, 95e′ and 95f′ for switching.
According to the image forming apparatus that uses the stationary developer units 31′, 32′, 33′ and 34′, the stationary developer units 31′, 32′, 33′ and 34′ are stationary, thus not movable to contacted with, or to be isolated from the photoreceptor body. Accordingly, a deterioration of printing quality and a lifespan of the photoreceptor body due to a contacting shock is improved, while a complicated construction using wiring harnesses is simplified by using the coupling PCB 95 as a power supply apparatus. However, problems still remain because of the complicated construction due to the wiring harnesses required to supply power from the HVPS 90′, the connecting lines patterned in the PCB 95, and the contact-points for high voltage switching. Further, noise from an application of high voltage occurs during a change from one stationary developer unit 31′, 32′, 33′ or 34′ to another stationary developer unit 31′, 32′, 33′ or 34′, and a reliability in switching of the high voltage contact-points deteriorates.